Transparent or translucent domes or skylight structures of various kinds are currently in use in buildings throughout the world. Such structures are generally provided in a portion of a roof, allowing sunlight to pass through the skylight portion of the roof and illuminate interior regions of the building. Skylights have gained increasing usage in recent years due to the energy conservation which they afford.
Fire safety criteria have also become increasingly important in recent years, due at least in part to increased density in urban areas. The American Society for the Testing of Materials has established criteria for rating the performance of roofing materials subjected to fire conditions which are published in ASTM E-108 (1983) entitled, "Tests For Fire Resistance of Roof Covering Materials." The highest rating awarded is "Class A" which indicates that the skylight is effective against severe fire exposures. To receive a Class A rating, the skylight must pass each of the Intermittent-Flame Test of Section 5, the Spread-of-Flame Test of Section 6, and the Burning-Brand Test of Section 7.
The Intermittent-Flame Test requires the skylight structure to withstand an intermittent luminous gas flame applied to its upper side for fifteen two-minute cycles without sustained flaming on its underside, production of flaming or glowing brands, displacement of portions of the test sample, or exposure or falling away of portions of the structure.
The Spread-of-Flame Test requires the skylight structure to withstand a continuous luminous gas flame applied thereto for 10 minutes, or until flaming of the material being tested permanently recedes from a point of maximum spread, whichever is shorter. The structure is then examined for distance to which the flame has spread, production of glowing brands, and displacement of portions of the structure.
The Burning-Brand Test requires the skylight structure to withstand a burning brand consisting of a grid 12 inches square and approximately 2 1/4 inches thick, made of kiln-dried Douglas fir lumber. The brand is made of 36 strips of lumber each 3/4 inch by 3/4 inch square by 12 inches long, placed in three layers of 12 strips each, with strips placed 1/4 inch apart. The brand is ignited on all sides and subsequently placed on the surface of the skylight structure at the location considered most vulnerable. The burning brand remains on the skylight structure until it is consumed and until all evidence of flame, glow, and smoke has disappeared. During and after the test, the structure is examined for the appearance of sustained flaming on its underside, production of flaming or glowing brands, displacement of the test sample, and the exposure or falling away of portions of the roof deck. Glowing material falling through the skylight structure is unacceptable.
One plastic skylight structure which has been found to meet these criteria consists of a pair of thermoset resin fiberglass sheets bonded on either side of a grid core formed of aluminum beams, with the spacing between the sheets filled in by fiberglass insulation. This arrangement has been found to suffer from numerous shortcomings; most principally, the efficiency of light transmission, the weathering performance, the impact strength and the use of adhesive bond for their performance.
It is desirable to provide a skylight structure having plastic panels which is capable of satisfying the aforementioned fire safety criteria, while providing greater performance such as better light transmission than current designs, weathering, and impact strength. Moreover, it is desired to provide such a skylight structure which is also inexpensive and easy to assemble.